Traffic deaths rose, then fell, after three states legalized marijuana

Traffic deaths rose temporarily in three states that approved recreational marijuana, according to a new study. This research is the latest attempt to untangle the question of whether legal marijuana makes the roads more dangerous.

Currently, 33 states have legalized medical marijuana and 10 have legalized recreational marijuana. Though the public is increasingly accepting of cannabis, experts worry about negative public health effects, given a growing body of research that says marijuana impairs driving abilities and the fact that there’s no accurate way to measure how impaired someone is from cannabis. A study published today in the journal Addiction found that, on average, Colorado, Oregon, and Washington state (all of which have legalized medical marijuana) had about one additional traffic death per million residents. The same effect was true for the neighboring states, probably because people drive across state lines to buy cannabis. In total, there were about 170 extra deaths in the first six months after legalization.

Interestingly, the increase was temporary, and rates went back to normal after about a year. Though the study wasn’t designed to explain this result, it could be that legalizing recreational marijuana initially leads to an increase in newer, more inexperienced users, says study co-author Tyler Lane, a post-doc in the School of Public Health and Preventive Medicine at Monash University in Australia.